Re: [PATCH v1] usb: typec: tcpm: Check for port partner validity before consuming it

[Badhri Jagan Sridharan]

On Sat, Apr 27, 2024 at 12:23 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
>
> On Sat, Apr 27, 2024 at 05:50:10PM +0000, Badhri Jagan Sridharan wrote:
> > typec_register_partner() does not guarantee partner registration
> > to always succeed. In the event of failure, port->partner is set
> > to the error value or NULL. Given that port->partner validity is
> > not checked, this results in the following crash:
> >
> > [17514.377076][  T275] Unable to handle kernel NULL pointer dereference at virtual address 00000000000003c0
> > [17514.378270][  T275] pc : run_state_machine+0x1bc8/0x1c08
> > [17514.378286][  T275] lr : run_state_machine+0x1b90/0x1c08
> > ..
> > [17514.378377][  T275] Call trace:
> > [17514.378381][  T275]  run_state_machine+0x1bc8/0x1c08
> > [17514.378388][  T275]  tcpm_state_machine_work+0x94/0xe4
> > [17514.378396][  T275]  kthread_worker_fn+0x118/0x328
> > [17514.378406][  T275]  kthread+0x1d0/0x23c
> > [17514.378412][  T275]  ret_from_fork+0x10/0x20
>
> Nit: thre is little use in the timestamps and the T275 tag. In future
> patches you can safely ommit such data.
>
> >
> > To prevent the crash, check for port->partner validity before
> > derefencing it in all the call sites.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: c97cd0b4b54e ("usb: typec: tcpm: set initial svdm version based on pd revision")
> > Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
> > ---
> >  drivers/usb/typec/tcpm/tcpm.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index ab6ed6111ed0..8a4fa8d875c6 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -4,7 +4,6 @@
> >   *
> >   * USB Power Delivery protocol stack.
> >   */
> > -
> >  #include <linux/completion.h>
> >  #include <linux/debugfs.h>
> >  #include <linux/device.h>
> > @@ -1580,7 +1579,8 @@ static void svdm_consume_identity(struct tcpm_port *port, const u32 *p, int cnt)
> >       port->partner_ident.cert_stat = p[VDO_INDEX_CSTAT];
> >       port->partner_ident.product = product;
> >
> > -     typec_partner_set_identity(port->partner);
> > +     if (!IS_ERR_OR_NULL(port->partner))
>
> I think that it might be better to check typec_register_partner() result
> in tcpm_typec_connect() and skip setting port->partner in case it
> returned an error (an error message would be also beneficial).
> See for example, how this is handled in ucsi_register_partner().
>
> Then these checks can be turned into simple `if (port->partner)`.


Sounds good ! However, I was wondering whether the error message is
redundant as typec_register_partner() also prints one. I have anyways
added that in V3.

Thanks,
Badhri

>
> > +             typec_partner_set_identity(port->partner);
> >
> >       tcpm_log(port, "Identity: %04x:%04x.%04x",
> >                PD_IDH_VID(vdo),
> > @@ -1742,6 +1742,9 @@ static void tcpm_register_partner_altmodes(struct tcpm_port *port)
> >       struct typec_altmode *altmode;
> >       int i;
> >
> > +     if (IS_ERR_OR_NULL(port->partner))
> > +             return;
> > +
> >       for (i = 0; i < modep->altmodes; i++) {
> >               altmode = typec_partner_register_altmode(port->partner,
> >                                               &modep->altmode_desc[i]);
> > @@ -4244,7 +4247,8 @@ static void tcpm_typec_connect(struct tcpm_port *port)
> >               port->partner = typec_register_partner(port->typec_port,
> >                                                      &port->partner_desc);
> >               port->connected = true;
> > -             typec_partner_set_usb_power_delivery(port->partner, port->partner_pd);
> > +             if (!IS_ERR_OR_NULL(port->partner))
> > +                     typec_partner_set_usb_power_delivery(port->partner, port->partner_pd);
> >       }
> >  }
> >
> > @@ -4323,8 +4327,10 @@ static void tcpm_typec_disconnect(struct tcpm_port *port)
> >       port->plug_prime = NULL;
> >       port->cable = NULL;
> >       if (port->connected) {
> > -             typec_partner_set_usb_power_delivery(port->partner, NULL);
> > -             typec_unregister_partner(port->partner);
> > +             if (!IS_ERR_OR_NULL(port->partner)) {
> > +                     typec_partner_set_usb_power_delivery(port->partner, NULL);
> > +                     typec_unregister_partner(port->partner);
> > +             }
> >               port->partner = NULL;
> >               port->connected = false;
> >       }
> > @@ -4549,6 +4555,9 @@ static enum typec_cc_status tcpm_pwr_opmode_to_rp(enum typec_pwr_opmode opmode)
> >
> >  static void tcpm_set_initial_svdm_version(struct tcpm_port *port)
> >  {
> > +     if (IS_ERR_OR_NULL(port->partner))
> > +             return;
> > +
> >       switch (port->negotiated_rev) {
> >       case PD_REV30:
> >               break;
> >
> > base-commit: 3f12222a4bebeb13ce06ddecc1610ad32fa835dd
> > --
> > 2.44.0.769.g3c40516874-goog
> >
>
> --
> With best wishes
> Dmitry